Geared turbofan engines may use journal bearings in the gear systems. Journal bearings operate using a film of oil. As a result, geared turbofan engines use larger oil systems than direct-drive turbofan engines. The oil system for the geared engine may be twice the size of the oil system for a direct drive system. A larger oil system may result in a higher weight.
The oil used in a fan drive gear system (FDGS) is typically cooler than oil in other parts of the engine. To maintain oil at temperatures suitable to the FDGS, multiple coolers may be used. For example, one air-oil heat exchanger and one fuel-oil heat exchanger may be installed to cool oil for an FDGS. However, by adding a second oil cooler, additional volume in the engine is consumed and the weight of the engine is increased.